In a cellular communication system, a model in which mobile stations 102 are disposed within a cell 101 centering on a base station 100 as illustrated in FIG. 8 is supposed. Also, in a cellular communication system, a structure in which a cell is divided into a plurality of zones (called sectors) 101-1 to 101-n (n is an integer equal to or more than 2, and n=3 in FIG. 9), and a directional antenna apparatus (hereinafter, sector antenna) 110-i is provided for each sector 101-i (i=1 to n) as illustrated in FIG. 9 is used. In other words, in the example of FIG. 9, the sector antenna 110-i performs beam formation to cover each sector 101-i as a wireless zone and performs communications with the mobile station 102 which is located within the sector 101-i. 
If such zone division is performed by the sector antenna 110-i (directional beam) as described above, due to difference of an antenna gain, influence of interference waves of other directions than a desired direction can be reduced, and influence of interference waves of other sectors 101-i can also be reduced.
In such a cellular communication system, a redundant structure is formed to cope with a situation that a signal receiving circuit of the sector antenna 110-i is out of order. As a representative redundant structure, there is an NE structure (for example, see Patent Document 1). In the NE structure, an operating system (normal: N) which is used during a normal operation and a preliminary system (emergency: E) which is used when the operating system cannot normally operate due to a failure are formed, and when the operating system is out of order, processing is performed by switching to the preliminary system.
[Patent Document 1] Japanese Laid-open Patent Publication No. 5-268196
However, such a redundant structure requires a complicate control algorithm or a preliminary circuit to be provided in advance only to cope with a failure, which is a wasteful component, and increases the cost.
Further, there occurs the following problem. In a cellular communication system, a mobile station (hereinafter, “terminal”) located in the vicinity of a sector boundary undergoes characteristics deterioration in an uplink (direction from a mobile station to a base station apparatus) communication. In other words, in the vicinity of a sector boundary, a signal of an adjacent sector functions as an interference wave, and thus a signal received from this zone becomes deteriorated and has a low reception quality. As a result, retransmission is frequently required, so that the throughput is lowered. If the throughput of terminals located in the vicinity of a sector boundary remains lowered, the terminal throughput of the entire sector and accordingly the entire cell is also lowered. This is a problem which has to be resolved even in the viewpoint of cell coverage.